December is a month of stark contrasts and profound transitions. In the Northern Hemisphere, it marks the descent into winter's depths, while in the Southern Hemisphere, it heralds the brilliance of summer. This duality is mirrored in its birthstones—a trio of gems that span a spectrum of color, from the sky-blue of turquoise to the fiery brilliance of zircon and the deep violet-blue of tanzanite. These stones are not merely decorative; they are steeped in centuries of human history, geological wonder, and cultural symbolism. As the modern calendar year draws to a close, the December birthstones offer a final, brilliant chapter in the story of gemstones, each with a unique narrative of formation, discovery, and meaning.
The assignment of these specific stones to December is a relatively modern convention, solidified in the early 20th century. Yet, their individual histories stretch back millennia. Turquoise, one of the oldest known gemstones, has been cherished by civilizations across the globe for its protective and fortunate qualities. Zircon, often confused with synthetic cubic zirconia, boasts a history of its own as a prized gemstone with exceptional fire. Tanzanite, the youngest of the trio, is a geological marvel of the 20th century, found in only one location on Earth. Together, they represent a fascinating cross-section of gemology: a hydrated phosphate, a silicate mineral, and a variety of the mineral zoisite. This article will delve into the rich history, geological origins, and distinctive properties of these three December gems, providing a comprehensive guide for enthusiasts, collectors, and anyone captivated by the science and lore of the mineral kingdom.
The Traditional Stone: Turquoise
Turquoise holds the distinction of being the traditional December birthstone, a title it has carried for centuries. Its name, derived from the French pierre turquoise meaning "Turkish stone," hints at its historic trade routes from the Persian mines to Europe via Turkey. However, its use predates these trade networks by thousands of years, with archaeological evidence pointing to ancient Egypt, Mesopotamia, and the American Southwest as early centers of its use.
History and Lore
The lore surrounding turquoise is vast and varied, often centered on its perceived protective and fortunate properties. The provided sources explicitly state that turquoise is "considered a symbol of good fortune and success." This belief is not a modern invention but a continuation of ancient traditions. In many cultures, it was believed to be a talisman that could ward off evil and protect the wearer from harm. Its sky-blue color was often associated with the heavens, making it a sacred stone in various spiritual practices. While the sources do not detail specific historical events or figures associated with turquoise, its enduring status as a traditional birthstone underscores its deep-rooted significance in Western gemology.
Geological Formation and Sources
Turquoise is a secondary mineral formed when water containing copper and aluminum seeps through pre-existing rocks. This process is slow and occurs in arid regions, which is why turquoise deposits are typically found in dry, mountainous areas. The most famous historical sources include the ancient mines of Persia (modern-day Iran), which produced the highly prized "robin's egg blue" turquoise. In the United States, the Southwest—particularly Arizona and New Mexico—has been a major source for centuries, with Native American tribes like the Navajo, Zuni, and Hopi developing sophisticated silversmithing traditions around the stone. While the provided chunks do not specify modern mining locations, the historical significance of these regions is well-established in gemological literature.
Gemological Properties
Turquoise is an opaque, cryptocrystalline mineral with a chemical composition of CuAl₆(PO₄)₄(OH)₈·4H₂O (hydrated copper aluminum phosphate). Its color ranges from sky blue to bluish-green, primarily due to the presence of copper (blue) and iron (green). The gem's quality is often judged by its color, uniformity, and the presence of a "matrix"—a web of host rock that can be part of the stone's character. On the Mohs scale of hardness, turquoise ranks between 5 and 6, making it relatively soft and susceptible to scratching. It has a vitreous to waxy luster and is typically cut en cabochon to showcase its color. Due to its porosity and sensitivity to chemicals, it requires careful handling and cleaning.
The Fire of Zircon
Often overshadowed by its more famous synthetic counterpart, cubic zirconia, natural zircon is one of the oldest minerals on Earth and a brilliant gemstone in its own right. It is one of the three official December birthstones, valued for its exceptional brilliance and fire.
History and Lore
Zircon has a long and storied history, though the provided sources offer limited specific lore beyond its status as a December birthstone. Its use dates back to ancient times, and it has been found in archaeological sites across the globe. In the Middle Ages, zircon was believed to induce sleep, ward off evil spirits, and bring prosperity and honor. Its high refractive index and strong dispersion (fire) made it a popular diamond simulant long before the advent of modern synthetics. The sources note that zircon is "known for its brilliance and is often used as a diamond substitute," a fact that underscores its historical and ongoing appeal in jewelry.
Geological Formation and Sources
Zircon is a silicate mineral (ZrSiO₄) that forms as a primary crystal in igneous and metamorphic rocks. It is exceptionally durable and resistant to weathering, which is why it is often found in sedimentary deposits as well. Zircon crystals are found worldwide, with significant commercial sources in Australia, Thailand, Sri Lanka, and Cambodia. The sources do not specify modern mining locations, but zircon's global distribution is a well-documented fact in geology. Its formation under high temperatures and pressures makes it a valuable tool for geochronology, as it can trap uranium and lead atoms, allowing scientists to date the age of rocks.
Gemological Properties
Zircon is a hard and durable gemstone, ranking 6.5 to 7.5 on the Mohs scale, making it suitable for various types of jewelry. Its chemical composition is ZrSiO₄ (zirconium silicate). Zircon occurs in a variety of colors, including blue, green, red, yellow, and brown. The most valued color is a vibrant blue, often achieved through heat treatment of brownish zircon. Its most remarkable property is its high refractive index (1.92-2.01) and strong dispersion (0.039), which give it exceptional fire and brilliance, rivaling that of diamond. Zircon is typically faceted to maximize these optical properties. However, it can be brittle due to its perfect cleavage in one direction, requiring careful cutting and setting.
The Modern Marvel: Tanzanite
Tanzanite is the newest member of the December birthstone family, a 20th-century discovery that has captivated the gem world with its unique color and singular origin.
History and Lore
Tanzanite's history is remarkably brief. It was first discovered in the 1960s in the Merelani Hills of northern Tanzania, near Mount Kilimanjaro. The sources confirm that tanzanite is "found only in Tanzania," a fact that contributes to its rarity and allure. Its journey to becoming a birthstone was facilitated by the gemstone and jewelry company Tiffany & Co., which recognized its potential and launched a major marketing campaign in the late 1960s, naming it after its country of origin. While the provided sources do not detail specific metaphysical beliefs, its rapid rise to prominence is a modern gemological success story. The sources describe it as "prized for its deep blue-violet hue," a color that is virtually unique to this gem.
Geological Formation and Sources
Tanzanite is a variety of the mineral zoisite, specifically the blue to violet-blue variety. Its formation is a geological rarity. The conditions required to create tanzanite are so specific that it is believed all commercial deposits are confined to a small area of just a few square kilometers in the Merelani Hills. The process involves the metamorphism of the host rock under high heat and pressure, a phenomenon that is unlikely to have occurred elsewhere on Earth. This extreme rarity is a key part of its value proposition. The sources explicitly state its exclusive origin, making it a true "one-source" gemstone.
Gemological Properties
Tanzanite is a relatively soft gemstone, with a hardness of 6 to 7 on the Mohs scale, similar to quartz. Its chemical composition is Ca₂Al₃(SiO₄)₃(OH) (calcium aluminum hydroxyl silicate). The most striking feature of tanzanite is its pleochroism—displaying different colors when viewed from different crystal directions. It can appear blue, violet, and burgundy-red, depending on the orientation. Most tanzanite is heat-treated to enhance its blue color, as natural blue tanzanite is rare. It is almost always cut as a faceted gem to showcase its brilliance and color play. Due to its relative softness and perfect cleavage, it requires protection from knocks and careful cleaning.
Comparative Analysis and Care
The three December birthstones present a fascinating study in contrasts. While all are valued in jewelry, their physical and gemological properties dictate different uses and care requirements.
| Property | Turquoise | Zircon | Tanzanite |
|---|---|---|---|
| Chemical Family | Hydrated Phosphate | Silicate | Silicate (Zoisite) |
| Hardness (Mohs) | 5 - 6 | 6.5 - 7.5 | 6 - 7 |
| Color | Sky blue to bluish-green | Wide range (blue, brown, etc.) | Blue-violet (pleochroic) |
| Key Characteristic | Opaque, often with matrix | High brilliance & fire | Strong pleochroism |
| Typical Cut | Cabochon | Faceted | Faceted |
| Durability | Low (soft, porous) | Moderate (brittle, cleavage) | Moderate (cleavage) |
For collectors and wearers, understanding these differences is crucial for proper care. Turquoise, being the softest and most porous, should be cleaned with a soft, dry cloth. Avoid chemicals, ultrasonic cleaners, and prolonged exposure to water or oils, which can damage the stone or its stabilizing treatments. Zircon, while harder, is brittle and can fracture if knocked. It is sensitive to heat, so extreme temperature changes should be avoided. Cleaning with warm soapy water and a soft brush is safe, but ultrasonic and steam cleaners are not recommended. Tanzanite, with its perfect cleavage, is also vulnerable to blows. It should be cleaned with warm soapy water and a soft brush, avoiding harsh chemicals and sudden temperature changes. For all three, removing jewelry during strenuous activities is a wise precaution.
Conclusion
The December birthstones—turquoise, zircon, and tanzanite—offer a remarkable spectrum of color, history, and geological origin. From the ancient, sky-hued talisman of turquoise to the brilliant, ancient fire of zircon and the modern, singular beauty of tanzanite, each gem tells a distinct story. Their selection as birthstones reflects a blend of tradition and modernity, bringing together stones from different eras and continents. For the gemstone enthusiast, they represent a study in diversity: in formation, in properties, and in cultural significance. Whether valued for historical lore, exceptional brilliance, or unique geographic origin, these three gems provide a brilliant finale to the year, each a testament to the Earth's incredible ability to create beauty under pressure and time.